Preferential oxidation reactor temperature regulation

ABSTRACT

According to the present invention, a temperature profile within a preferential oxidation reactor is controlled using a two phase water/steam system to provide a temperature range within the reactor ( 10 ) which favors the selective oxidation of CO in a hydrogen rich reformate stream. The reformate is flowed in a mixture with oxygen over a preferential oxidation catalyst ( 17 ). The temperature profile is controlled by flowing a stream of water proximate to the preferential oxidation catalyst ( 17 ) so as the stream of water and the reformate stream passing over the catalyst ( 17 ) are in a heat transfer arrangement. The stream of water is maintained as a two phase stream from a point at which the water reaches its boiling temperature to a point proximate an outlet from which the stream of water exits the reactor ( 10 ).

RELATED APPLICATIONS

[0001] The present invention claims priority of U.S. Provisional PatentApplication 60/388,555 filed Jun. 13, 2002 and U.S. Patent Application09/562,787 filed May 2, 2000 which claims priority of U.S. ProvisionalPatent Applications 60/132,184 and 60,132,259, both filed May 3, 1999.

TECHNICAL FIELD

[0002] The present invention is generally related to a hydrocarbon fuelreforming system for reforming a gaseous or liquid hydrocarbon fuel toproduce a hydrogen-rich product stream for use in, among other things,fuel cells. More particularly, the invention is directed to a method andapparatus for selective or preferential oxidation of carbon monoxide,and particularly in the control of reactor temperature during thisprocess.

BACKGROUND OF THE INVENTION

[0003] Reforming of hydrocarbon fuels to make hydrogen is well known inthe art. In a first stage, hydrocarbons are reacted with steam to make amixture of hydrogen, carbon monoxide and other components, commonlyreferred to as the reformate, sometimes also referred to as syngas,particularly before a water-gas shift reaction is performed. In a secondstage, known as the water-gas shift reaction, the reformate is treatedwith additional steam to convert most of the carbon monoxide to carbondioxide and produce additional hydrogen. However, the shift reaction isan equilibrium reaction, and typically does not reduce the carbonmonoxide content of the reformate to a level suitable for supplying to aPEM fuel cell. For a PEM fuel cell, it is necessary to further removecarbon monoxide from the hydrogen-rich reformate stream. It is known tofurther reduce the carbon monoxide content of hydrogen-rich reformateexiting a shift reactor by a so-called preferential oxidation (“PrOx”)reaction (also known as “selective oxidation”) effected in a suitablePrOx reactor. A PrOx reactor usually comprises a catalyst that promotesthe selective oxidation of carbon monoxide to carbon dioxide by oxygenin the presence of the hydrogen, without oxidizing substantialquantities of the hydrogen itself. The preferential oxidation reactionis:

CO+½O₂−CO₂  (1)

[0004] Desirably, the amount of O₂ used for the PrOx reaction will be nomore than about two times the stoichiometric amount required to reactthe CO in the reformate. If the amount of O₂ exceeds about two to threetimes the stoichiometric amount needed, excessive consumption of H₂results. On the other hand, if the amount of O₂ is substantially lessthan about two times the stoichiometric amount needed, insufficient COoxidation may occur, making the reformate unsuitable for use in a PEMfuel cell. The essence of the PrOx process is described in theliterature, for example, in U.S. Pat. Nos. 1,366,176 and 1,375,932.Modern practice is described, for example, in, “Preferential Oxidationof CO over Pt/γ-Al₂O₃ and Au/α-Fe₂O₃: Reactor Design Calculations andExperimental Results” by M. J. Kahlich, et al. published in the Journalof New Materials for Electrochemical Systems, 1988 (pp.39-46), and inU.S. Pat. No. 5,316,747 to Pow et al.

[0005] A wide variety of catalysts for promoting the PrOx reaction areknown. Some are disclosed in the above references. In modern practice,such catalysts are often provided by commercial catalyst vendors, andtheir compositions are typically proprietary. The practitioner isinstead provided with approximate temperature ranges for use, and somephysical parameters. The properties of candidate catalysts have to beevaluated in the actual proposed design before final selection of acatalyst for development or production. Moreover, catalysts come in awide variety of physical forms. In addition to the “classical” pelletsand powders, which are typically porous to some extent, catalysts arealso supplied on any of a large variety of supports. These may also bepellets, but also include monoliths, such as the ceramic and metalhoneycombs used in automotive catalytic converters, metal and ceramicfoams, and other monolithic forms.

[0006] PrOx reactions may be either (1) adiabatic (i.e., where thetemperature of the reformate and the catalyst are allowed to rise duringoxidation of the CO), or (2) isothermal (i.e., where the temperature ofthe reformate and the catalyst are maintained substantially constantduring oxidation of the CO). The adiabatic PrOx process is typicallyeffected via a number of sequential stages which progressively reducethe CO content. Temperature control is important at all stages, becauseif the temperature rises too much, methanation, hydrogen oxidation, or areverse shift reaction can occur. The reverse shift reaction producesmore undesirable CO, while methanation and hydrogen oxidation decreasesystem efficiencies.

[0007] The selectivity of the catalyst of the preferential oxidationreaction is dependent on temperature, typically decreasing inselectivity as the temperature rises. The activity of the catalyst isalso temperature dependent, increasing with higher temperatures.Furthermore, the reaction is very slow below a threshold temperature.For this reason the temperature profile in a PrOx reactor is importantin maximizing the oxidation of carbon monoxide while minimizing theundesired oxidation of the hydrogen gas in the mixed gas stream.

[0008] More particularly, when the PrOx catalyst temperature is lessthan a certain value, high levels of CO may bind to the catalytic sitebut fail to react, thereby inhibiting the catalyst's performance. WhenPrOx temperature increases beyond a certain point, catalyst selectivitydecreases, and a higher equilibrium CO concentration results. Because ofthese multiple sensitivities of the reaction to temperature, there isfor any catalyst a preferred temperature range for efficient operation.Moreover, to minimize catalyst volume, it is often desirable to performa first step of the preferential oxidation at a higher temperature, forspeed of reaction, and a final cleanup at a lower temperature, forselectivity and for minimum reverse shift.

[0009] The need for temperature control adds numerous complexities tothe system. For example, multiple air lines, air distributors, air flowcontrollers, and reactor vessels, as disclosed, for example, in U.S.Pat. No. 5,874,051, add size and manufacturing cost to the reactor, andfurther highlight the need for a compact, efficient reactor design.Compactness, simplicity, and efficiency are particularly important insmall scale PrOx reactors suitable for use in mobile and domestic-scalesystems.

[0010] The present invention addresses the above problems andchallenges, and provides other advantages, as will be understood bythose in the art, in view of the following specification and claims.

SUMMARY OF THE INVENTION

[0011] According to one aspect of the invention, a method of controllinga temperature profile within a preferential oxidation reactor to providea temperature range within the reactor which favors the selectiveoxidation of CO in a hydrogen rich reformate stream by a preferentialoxidation catalyst is provided. It includes flowing a stream of amixture of a hydrogen rich reformate and oxygen over the preferentialoxidation catalyst. A stream of water is flowed proximate to thepreferential oxidation catalyst so as the stream of water and thereformate stream passing over the catalyst are in a heat transferarrangement. The stream of water is maintained as a two phase streamfrom a point at which the water reaches its boiling temperature to apoint proximate an outlet from which the stream of water exits thereactor.

[0012] According to another aspect of the invention, a reactor for theselective oxidation of carbon monoxide in a hydrogen rich reformatestream includes a reactor body. The reactor has an inlet for theaddition of a reformate stream to the reactor body. The reactor alsoincludes at least one oxygen inlet for the addition of oxygen to thereformate stream. A catalyst suitable for selective oxidation of carbonmonoxide is located within the reactor body. The reactor includes a heatexchanger, having an inlet and an outlet, for removing heat from atleast one of the catalyst and the reformate. A stream of water flowsthrough the heat exchanger. The stream of water enters the heatexchanger at least partially as liquid water and is a two phase mixtureof water and steam throughout at least a portion of the reformate flowpath.

[0013] According to another aspect of the invention, a reactor for theselective oxidation of carbon monoxide in a hydrogen rich reformatestream includes a reactor body. The body includes an inlet for theaddition of a reformate stream to the reactor body. The reactor has atleast one inlet for the addition of oxygen to the reformate stream. Asubstrate, wash coated with a catalyst suitable for selective oxidationof carbon monoxide is contained within the reactor body and thesubstrate is a heat exchanger through which a coolant flows.

[0014] According to another aspect of the invention, a heat exchangerincludes two or more tubular sections each with an inlet and an outletfor permitting circulation of a heat exchange fluid through the tubularsection. The heat exchanger has a connector between each tubular sectionfor permitting a flow from the outlet of one tubular section to theinlet of the next tubular section.

[0015] According to another aspect of the invention, the operation ofPrOx reactors in purifying reformate, especially in small or mobilesystems, can be improved by particular improvements in management of thetemperature profile in the PrOx reactor. These improvements includeoperating the reactor in a substantially isothermal mode by using theparticular properties of two-phase cooling water, i.e., water/steammixtures, to maintain the temperature of the heat-removal system closeto the boiling point of water at a particular pressure. Moreover, thepressure may be adjusted by a pressure regulator to place the boilingtemperature at a favorable point in the temperature profile of theparticular catalyst used in the PrOx reaction. Additional improvementsinclude use of an initial non-catalytic heat-exchange section within thereactor to allow cooling of the reformate before beginning thepreferential oxidation reaction. Furthermore, adjustment of water flowrate can provide a significant final section of the reactor at a reducedtemperature to provide a final cleanup stage at slow kinetics butfavorable selectivity of the catalyst. In achieving these improvements,it is preferable, but not required, to use catalysts deposited onto orincorporated into monolithic structures, because of the improved heatexchange that this can provide, as well as for preventing catalystattrition during operation. In these improvements, it is preferable inmost situations to have the coolant pass through the reactor counter thedirection of flow of the reformate being treated. However, when theresulting CO concentration is sufficiently low for the intended usebecause the initial concentration was low or the final end use does notrequire an extremely low CO concentration, concurrent flow can beadvantageous in shortening the bed length by elimination of most of thecooler region of the reactor which has higher selectivity.

[0016] These and other aspects of the present invention set forth in theappended claims may be realized in accordance with the followingdisclosure with particular reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The following descriptions of the present invention are discussedwith particular reference to the appended drawings of which:

[0018]FIG. 1 is a perspective view of a PrOx reactor according to oneembodiment of the present invention;

[0019]FIG. 2 is a cross sectional view of the PrOx reactor of FIG. 1according to one embodiment of the present invention;

[0020]FIG. 3 is cross sectional view of a PrOx reactor according toanother embodiment of the present invention;

[0021]FIG. 4 is a qualitative plot of the temperature profile within thePrOx reactor of FIG. 3 according to another embodiment of the presentinvention;

[0022]FIG. 5 is a cross sectional view of a PrOx reactor according toanother embodiment of the present invention;

[0023]FIG. 6 is a qualitative plot of the temperature profile within thePrOx reactor of FIG. 5 according to another embodiment of the presentinvention;

[0024]FIG. 7 is a cross-sectional view of a PrOx reactor according toanother embodiment of the present invention;

[0025]FIG. 8 is a cross-sectional view of a heat exchanger componentaccording to another embodiment of the present invention;

[0026]FIG. 9 is a perspective view of a heat exchanger componentaccording to another embodiment of the present invention;

[0027]FIG. 10 is a front view of the heat exchanger component of FIG. 9;

[0028]FIG. 11 is a cross-sectional view of the heat exchanger componentof FIG. 10 along line 11;

[0029]FIG. 12 is a perspective view of a heat exchanger componentaccording to another embodiment of the present invention;

[0030]FIG. 13 is a top view of a heat exchanger component according toanother embodiment of the present invention;

[0031]FIG. 14 is a cross-sectional view of the heat exchanger componentof FIG. 13 along line 14;

[0032]FIG. 15 is top view of a portion of a heat exchanger according toanother embodiment of the present invention;

[0033]FIG. 16 is front view of a heat exchanger component according toanother embodiment of the present invention;

[0034]FIG. 17 is a cut away top view of the heat exchanger component ofFIG. 16 along line 17;

[0035]FIG. 18 is an exploded view of a PrOx reactor according to anotherembodiment of the present invention; and

[0036]FIG. 19 is a schematic view of fluid flow through the reactor ofFIG. 18.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0037] While the invention is susceptible of embodiment in manydifferent forms, there is shown in the drawings and will herein bedescribed in detail preferred embodiments of the invention. It is to beunderstood that the present disclosure is to be considered as anexemplification of the principles of the invention. This disclosure isnot intended to limit the broad aspect of the invention to theillustrated embodiments.

[0038] In appreciating the significance of the improvements describedherein, it should be recalled throughout that the temperature of thePrOx reactor catalyst is preferably maintained above a lower level, andbelow a maximum level so that the selectivity for carbon monoxideoxidation over hydrogen oxidation is maintained. At the same time, thevolume of the catalyst bed should be as small as possible, and thesystem should have as few parts as possible for ease of manufacturing.The PrOx reactors of the present invention incorporate and embodyimprovements with respect to balancing these conflicting requirements.

[0039]FIGS. 1 and 2 show a first embodiment of the present invention.The reactor 10 is shown in perspective in FIG. 1, and in cross sectionin FIG. 2. The reactor 10 includes a reactor body 11. A reformate inlet12 has an air inlet 14, through which an oxygen-containing gas (eitherpure oxygen, or oxygen mixed with other gases, such as in air) is mixedwith the reformate prior to entering the reactor 10. Alternatively, inother embodiments, the air inlet is directed into the reactor whereinoxygen is mixed with the reformate stream at a location inside thereactor body 11. Oxygen and air are generally used as synonyms herein,except in discussing particular chemical reactions. The rate of flow ofthe oxygen is usually controlled, and the flow may be adjusted tomaintain a desired ratio between the amount of carbon monoxide enteringthe reactor 10 and the amount of oxygen. The desired ratio isapproximately two oxygen atoms (i.e., one diatomic oxygen molecule) percarbon monoxide molecule. The reformate and oxygen mixture enters thereactor 10 and flows into a catalyst bed 17. The catalyst bed 17 isoptionally, and preferably, preceded by a non-catalytic cooling bed 16optimized for temperature equilibration of the reformate. In the designof FIGS. 1 and 2, the cooling bed 16 is preferably filled withheat-conducting material, such as metal shot, to optimize heat exchange,and the catalyst bed 17 is typically granular. Other physical forms arecontemplated, examples of which are discussed below.

[0040] The catalyst used may be any of those known in the art which aresuitable for the selective oxidation of carbon monoxide, examples ofwhich include Pt/γ-Al₂O₃ and Au/αFe₂O₃. A wide variety of catalysts forpromoting the PrOx reaction are known. Such catalysts are easilyavailable from commercial catalyst vendors, and their compositions aretypically proprietary. The approximate temperatures ranges for use, andthe physical parameters of the catalyst used may be any of thosecommonly used in the art. The properties of candidate catalysts have tobe evaluated in the actual proposed design before final selection of acatalyst for development or production. Moreover, catalysts come in awide variety of physical forms. In addition to classical porous pelletsand powders, catalysts on any of a large variety of supports aresuitable for use. These may be pellets, but also include monoliths, suchas the ceramic and metal honeycombs use in automotive catalyticconverters, metal and ceramic foams, and other monolithic forms, such ascatalyst coated on tubes of a heat exchanger, as described below. Thecatalysts may be coated onto the supports, or impregnated into them, ormay comprise extruded or otherwise formed catalyst-containing materials.Any of these catalyst chemistries and forms is potentially suitable forcatalyzing the PrOx reaction.

[0041] In this embodiment, the reformate flowing through the catalystbed 17 undergoes an exothermic preferential oxidation reaction in whichcarbon monoxide is selectively oxidized. In order to maintain atemperature that favors this reaction, a cooling tube 18 may be embeddedin the catalyst bed 17 and in the non-catalytic cooling bed 16.Depending upon the catalyst used, a favorable temperature for the PrOxreaction falls within the range of from about 75° C. to about 300° C.More preferably the temperature range should be from about 100° C. toabout 250° C. In one embodiment, a two phase water/steam cooling mediumis routed through the cooling tube 18 in a direction countercurrent tothe direction of flow of the reformate. Two phases are not necessarilypresent throughout the entire length of cooling tube 18, but are presentin at least a portion of the cooling tube 18 as it passes through thebeds 16 and 17. Water is typically fed to the reactor 10 in asubstantially single phase liquid form and is then at least partiallyvaporized by heat absorbed as it passes through cooling tube 18 withinthe reactor body 11, creating a two phase system. The point at which thewater is initially heated to its boiling point varies depending on theoperating conditions of the reactor 10. The point within the coolingtube 18 at which it reaches its boiling point may vary substantiallywithout affecting the carbon monoxide concentration present in thereformate exit stream from the reactor 10.

[0042] The two phase system is advantageous in that it allows theremoval of heat from the exothermic selective oxidation reaction withoutan increase in the temperature of the cooling medium. Rather, the heatremoved from the catalyst bed 17 performs work in the form of avaporization phase change. In this way, the reactor 10 is able to dealwith transitory power demands caused by, for example, an increased needfor hydrogen at a fuel cell (not shown) without the catalyst bed 17temperature rising to a point at which it does not operate effectivelyin the selective oxidation of carbon monoxide. To the extent that thewater in the cooling tube 18 is allowed to completely vaporize, thesteam within the cooling tube will become superheated to the temperatureof the reformate, and not operate effectively to reduce the temperatureof the reformate. In order to maintain a two phase system within thecooling tube 18, the flow of water through the cooling tube 18 isadjusted as needed to maintain some liquid water throughout most or allof cooling tube 18.

[0043] Controlling the pressure within the cooling tube 18 mayadditionally be used to maintain the temperature of the two phase system(by adjusting the boiling point of water). Water is inlet to the coolingtube 18 through inlet 42 and outlet at 44. The exiting stream ofwater/steam exits the reactor 10 and is then optionally integrated intothe larger fuel processing system of which the PrOx reactor 10 is apart. The steam may be directed to a steam separator, an auxiliaryheater, a heat exchanger, or a steam reformer located separately fromthe PrOx reactor. In this manner the efficiency of the system ismaximized by using heat generated in the exothermic selective oxidationreaction in other areas of the fuel processing system requiring theaddition of heat or steam. It should be noted that if the water isentirely evaporated in the final portion of its flow path through thereactor, such as in cooling bed 16, the temperature control desired canstill be obtained.

[0044] Referring to FIG. 2, upon exiting the catalyst bed 17, thereformate mixture flows into a manifold 20 where it is optionally andpreferably mixed with a second addition of oxygen from air inlet 22. Theamount of oxygen added through inlet 22 is generally in the range offrom about 10% to about 30%, or sub-ranges therein, preferably about20%, of the initial amount added through inlet 14. The mixture flowsinto catalyst bed 24 located annularly interior to gap 26 which containsthe first catalyst bed 17, and through which the first cooling tube 18is routed. The catalyst 24 may be any of the well known PrOx catalystsas discussed above. Here the mixture again undergoes the exothermicselective oxidation reaction. The reaction is preferably allowed toproceed adiabatically in catalyst bed 24. The now CO-depleted mixtureflows out of catalyst bed 24, through a second set of cooling coils 28which are optionally surrounded by additional PrOx catalyst oradditional steel shot. The cooling coils 28 are coiled around acylindrical central region 30. The central region 30 is blocked off, andmay be hollow, contain insulation, or may have additional reformingequipment contained therein. After passing through catalyst bed 24, thereformate flows into manifold 32 where it is directed out of the reactorthrough outlet 40.

[0045] Cool water enters the second set of coils 28 through inlet 34. Ittravels through the cooling coils 28, travels through a riser 36, andexits the reactor 10 through outlet 38. Outlet 38 is optionally andpreferably connected to water inlet 42. In traversing the reactor 10,the water of the cooling coils 28 is preferentially heated from an inlettemperature in the range of from about 20° C. to 60° C. to an outlettemperature of about 90° C. to about 120° C. This part of the coolantflow is substantially a single phase liquid. The water exiting fromoutlet 38 is optionally recycled to the inlet 42 of the highertemperature section. However, a fresh feed of water to inlet 42 may beused in addition, or in place of the water from outlet 38.

[0046] In addition to adjusting the temperature of the reformate to besuitable for use with the particular catalyst, the temperature may alsobe regulated to prevent condensation of water from the reformate ontothe catalysts. Alternatively, the moisture content of the reformate canbe reduced, for example by provision of a condenser, or by adjustment ofthe steam to carbon ratio, to prevent condensation in the beds.

[0047]FIG. 3 shows another embodiment of the present invention whereinthe PrOx reactor 60 includes the use of a two phase water coolingsystem. The water/steam is contained within a helical tube 62. Here, thehelical tube 62 coils around a central core 64 that is a hollow spacecontained within a sealed chamber.

[0048] In other embodiments, core 64 may contain an insulating material,a heat exchanger, or another reforming reactor module for preparation ofa hydrocarbon fuel for use in a PEM fuel cell. In one embodiment, thereforming reactor module includes a Low Temperature Shift (LTS) modulelocated in core 64. A LTS module is preferred in that it is temperaturecompatible with a PrOx reactor, and additionally, the reformate caneasily be routed directly from the LTS module to an inlet of a PrOxreactor.

[0049] The reactor has a reformate inlet 70 to which is suppliedreformate having a temperature typically within the range of from about250° C. to about 350° C. The helical tube 62 is typically constructed ofcopper or stainless steel. The helical tube 62 is surrounded by fins 66creating a first tube/fin assembly 68. Additional tube/fin assembliesmay be provided. The fins 66 are preferably constructed of a corrosionresistant material capable of withstanding the operating temperatures ofthe system. The preferred shapes for the fins 66 are square orrectangular, although other shapes could easily be substituted. Thenumber of fins 66 in this embodiment is sixteen per inch, although alesser or greater number could be substituted as desired depending onthe details of system design. The fins 66 are preferably affixed to thetube/fin assembly 68. This may be done by silver soldering, nickelbrazing, or press fitting the fins onto the tubes, with or withoutflanges or washers, to affix the fins 66 in place. The tube/fin assembly68 may be treated to prevent corrosion, for example, by plating withnickel or other corrosion-resistant material.

[0050] Any or all of the fins and tubing may be wash-coated with a PrOxcatalyst. As discussed above, many suitable catalysts exist forperforming the PrOx reaction. It is preferred that a catalyst whichdisplays optimal activity and selectivity for reacting CO withoutsubstantially reacting hydrogen throughout the operating temperaturerange is selected. A typical catalyst is a group VIII metal, orsometimes a Group VIB or VIIB metal, usually with selectivity promotersbased on non-noble metals or metal oxides.

[0051] In this embodiment, the helical tube 62 and the fins 66 arecontained between a cylindrical outer tube 74 and cylindrical inner core64 which are concentrically arranged. Moving axially down the passage 78formed between the outer tube 74 and inner core 64, the reactor of thisembodiment contains three sections, A, B, and C. Reformate and oxygenenter section A through inlet 70, where they are cooled by passing overthe helical tube 62 which contains two phase water/steam. Thetemperature of the reformate is lowered to be in the range of from about100° C. to about 200° C. Section A of the reactor 60 does not includecatalyst. Passing through section A lowers the temperature of thereformate to a temperature more favorable for the selective oxidationreaction.

[0052] The tube/fin assembly 68 within section B of the reactor 60 iswash coated with a selective oxidation catalyst. The washcoatingembodiment of this embodiment is preferred in many cases, especiallymobile applications, because it is more durable and resistant toattrition than pellets. Moreover, the catalyst will operate at atemperature very close to that of the coolant, improving control ofreaction temperatures. However, other physical forms of the catalyst mayalso be used, particularly catalyst-coated foams or monoliths, or evenpellets in stationary applications.

[0053] The reformate undergoes the exothermic selective oxidationreaction in section B and raises the temperature of the reformate asindicated qualitatively by dashed line 106 of FIG. 4. Sections A, B, andC of the reactor 60 of FIG. 3 correspond to sections A, B, and C of FIG.4. Helical tube 62 absorbs heat, and within the tube 62 water isvaporized to steam. The temperature of the helical tube 62 (and of theenclosing fins 66) remains substantially constant where the two phasesystem is maintained. The boiling point of the water is dependent onpressure, and the temperature of the steam/water mixture is maintainedat the boiling temperature as long as the two phases are present. Theoperating pressure within the helical tube 62 is generally maintained inthe range of from about 1 atmosphere to about 10 atmospheres. Thepressure within the tube remains essentially constant and is controlledby an external pressure regulating device, such as a variable speed orpressure pump, a regulator valve, an orifice, or functionally similarknown devices. Preferably, the cooling water is maintained as a onephase liquid, or a two phase liquid/vapor system substantiallythroughout at least sections B and C of the reactor 60.

[0054] Additional air may be added at inlet 76, and further selectiveoxidation of the reformate occurs in section C of the reactor 60. Theamount of air added through injector 76 is typically 10 to 30% of thetotal air introduced to the system, more preferably, about 20%. Airinjectors preferably inject the air through tubes having a plurality ofholes facing in a direction countercurrent to the flow of reformate toimprove mixing. Mixing may be enhanced if required throughout thereactor by the provision of mixing chambers, turbulence-creatingdevices, diffusing beds, and other known means. The specific location ofthe air inlets is different for other embodiments. Also, more or lessadditions may be present in a reactor. The temperature of the reformateincreases upon the selective oxidation caused by the second addition ofoxygen as indicated qualitatively by line 108. In other embodiments, noadditional air is added, and the temperature of the reformate continuesto decrease as it moves through the reactor with the temperature profileshown qualitatively by line 106. While FIG. 3 shows a reactor having twoair inlets, other embodiments may include more or less than two airinlets, or may include air bleeds. A final air bleed may be providedthrough inlet 80 and injector of distributor 81, proximate to the outlet82. This air is conveyed to a fuel cell downstream from a PrOx, where itoxidizes any CO adsorbed to the fuel cell membrane catalysts.

[0055] The total amount of oxygen added to the system is controlled by asingle controller (not shown) in response to the level of CO predictedby a system map of the reformer, or a measured value. In thoseembodiments having multiple oxygen feeds, the oxygen can be drawn from acommon source and distributed among the various feeds as a proportion ofthe whole. This may be done with calibrated orifices, delivering a fixedfraction of the total oxygen supply to each air inlet; or with valves orother equivalent methods well known in the art.

[0056] The rate of water fed to the helical tube 62 is controlled tomaintain a water/steam two phase system through at least reactor 60sections C and a substantial portion of B. In this way, the boilingtemperature of water, at the system pressure of the water, controls thetemperature profile of the principal reaction portion of the PrOxcatalyst, and of the reformate flowing over it, so as to maintain thetemperature in the optimal operating range of the particualr catalystbeing used. While the flow rate is adjusted as needed, it is generallypossible to maintain the flow rate at a constant level through a widerange of operating conditions, including varying system demands. Thepresence of two phase water makes the system resilient to transientpower demands. The point within the helical tube 62 at which the systembecomes a two phase system may vary substantially throughout the lengthof the reactor 60, particularly within sections A and B, with littleeffect on the final level of CO in the reformate, as long as at leastpart of the length contains the two phase water/steam mixture. Theoperating temperature of the reactor varies with position within thereactor. FIG. 4 is a schematic plot 100 showing qualitatively how thetemperature within the reactor 60 changes with position. The coolingwater/steam temperature within the helical tube 62 is indicated by thesolid line 104. The plotted embodiment assumes section A containstwo-phase water, with no significant length of the tube 62 containingpure steam. The reformate (gas-phase) temperature is qualitativelyindicated by the dashed line 106. The rise in line 106 at the beginningof section B is caused by the beginning of oxidation of the CO by theadded oxygen. Line 108 shows the qualitative temperature profile wherethe reactor 60 is receiving an oxygen injection through inlet 76. Line106 shows the temperature profile where there is only a single additionof oxygen to the reactor 60. The temperature profile of the reformate asit flows through the reactor is the same whether there are two oxygenadditions up to the point of the second addition. Therefore, thetemperature profile of both up to the point of the second addition, ifpresent, is indicated by line 106.

[0057]FIG. 5 shows another embodiment of a PrOx reactor 200. Reformateenters the reactor through a first inlet 202. The reformate preferablyenters the reactor after being cooled to a temperature in the range offrom about 60° C. to about 130° C., more preferably in the range of fromabout 70° C. to about 90° C. Cooling of the reformate prior to feedingto the reactor 200 precipitates out water vapor from the reformatestream, preventing the condensation of water from the reformate in thePrOx reactor or the PEM fuel cell. Other embodiments employ a waterremoval system (not shown) to remove water that may condense prior toentry, within the reactor, or between the reactor and a fuel cell stack.

[0058] Oxygen is added to the reformate through air inlet 204. The airis added at ambient temperature. In other embodiments, the air is addedseparately to a reactor and mixed with the reformate therein. Within thereactor 200, the reformate/air mixture flows over a catalyst bed 206.Here, the catalyst supported on a monolith or foam, typicallyreticulated, to provide better radial and axial heat transfer incomparison to a packed bed. In passing through the catalyst 206, the COpresent is selectively oxidized to carbon dioxide. Preferably, theamount of CO present is reduced to a level in which the reformate issuitable for use with a PEM fuel cell.

[0059] The catalyst 206 of the reactor 200 is distributed annularlyabout a core 208 within the reactor. A core may be hollow, containinsulation, be solid, or may contain another unit used in the processingof a hydrocarbon. The core 208 occupies the center of the reactor 200,and the catalyst bed is positioned radially outward beginning at theouter edge of the core 208, and extending towards the outer wall 210 ofthe reactor. The reactor 200 is jacketed with a cooling water jacket 212positioned within the outer wall 210. In other embodiments, thejacketing is not contained within a reactor wall, but either internal orexternal to the wall. The core 208 results in the selective oxidationreaction occurring generally closer to the cooling jacket 212, incontrast to a reactor not containing core region 208, and results in amore even temperature profile in a radial direction at each pointthroughout the catalyst bed 206. In other words, the temperature in thecatalyst bed 206 at any point having axially the same position, andradially a different position is closer to equal than without the use ofthe core 208.

[0060] Water enters the water jacket 212 through inlet 214. Thetemperature of the water is preferably in the range of from about 1° C.to about 70° C. In traversing the jacket 212, a portion of the waterbecomes heated to a temperature wherein it vaporizes to steam creating atwo phase system. The pressure within the jacket 212 is preferablymaintained in the range of from about 1 to about 10 atmospheres.Therefore, the boiling temperature of the water in the jacket may be attemperatures of about 100° C. to about 200° C., depending on thepressure in the jacket. Use of the two phase water system has theadvantage of allowing the temperature of the jacket 212 to remainsubstantially constant when the pressure is substantially constant,while still absorbing heat which is in turn used to vaporize liquidwater. By supplying the water at a rate and temperature sufficient toensure two phases throughout a portion of the reactor 200, control isexercised over the temperature within the catalyst 206. The reformatetravels through the catalyst 206 and exits the reactor 200 throughreformate outlet 216. The water/steam of the jacket 212 exits thereactor through outlet 218

[0061]FIG. 6 shows a graph 250 which charts the temperature profileobtained in the operation of a reactor according to the embodiment shownin FIG. 5. The horizontal axis 252 indicates position within thereactor, and the vertical access 254 qualitatively indicates thetemperature. Reformate temperature is indicated by line 256, where theleft hand side is the entry temperature, and the right hand side theexiting temperature. Cooling water flows countercurrent to the reformatestream, and enters on the right and exits on the left according to line258. The two phase vaporization of the cooling water occurs near or atpoint 260. The temperature of the two phase system stops increasing atthat point.

[0062] The PrOx reactor 200 of this example is especially suitable whenthe concentration of CO in the reformate has previously been reduced bya first PrOx reactor, for example one integrated with a reformer, sothat the reactor 200 is performing essentially a final cleanup function.It is also particularly suited to use with a fuel cell stack operatingat a temperature above that typically used in a PEM fuel cell which isabout 70° C. to about 85° C. Such a fuel cell stack may operate attemperature at from about 90° C. to about 150° C., which has becomepossible with the use of high-temperature tolerant PEM membranes and/ormembrane electrode assemblies.

[0063]FIG. 7 shows another embodiment of a PrOx reactor according to thepresent invention shown generally as reference numeral 300. The reactor300 preferably includes a reformate inlet 302 and a reformate outlet304. The reactor 300 preferably includes a core 306 positioned withinthe reactor body 308 such that reformate fed into the reactor throughthe reformate inlet 302 travels about the core 306 in traversing thereactor 300 to the reformate outlet 304. Air may be mixed with thereformate within the reformate inlet 302 prior to entry into the reactorbody 308. However, other embodiments may have air inlets positioned suchthat air may be injected into the reactor body in place of, or inaddition to the air added into the reformate inlet 302.

[0064] The reformate generally flows around the core 306 and over a heatexchanger 310 positioned within the reactor body 308. The heat exchangerwill now be described in greater detail in conjunction with FIGS. 8-16.

[0065] The heat exchanger 310 is generally comprised of a plurality ofmodular rings 312. A cross-sectional view of a single modular ring 312is shown in FIG. 8. Each ring 312 generally includes a tubular sectionwhich here is a flow tube 314. The flow tube 314 generally has acircular shape, but the shape is not limited, and could include suchshapes as oblong, obround, triangular, polygonal, or numerous othershapes with the same beneficial results. Each ring 312 generallyincludes an inlet 316 and an outlet 318 for permitting circulation of aheat exchange fluid. The preferred heat exchange fluid in thisembodiment is water or a water and steam mixture. However, numerous heatexchange fluids could be flowed through the flow tube 314. Stainlesssteel is the preferred material for forming the flow tube 314. Benefitsof stainless steel include its resistance to corrosion and its abilityto withstand heat and pressure.

[0066] The heat exchanger generally includes a connector between eachtubular section, or flow tube 314 for permitting flow from the outlet318 of one to the inlet 316 of another. The connector preferablyincludes a manifold 320. Each modular ring 312 generally includes asingle manifold 320 which directs fluid flow into, out of, and withineach modular ring 312. The manifold 320 is shown separately in FIGS.9-11. The manifold 320 generally includes a section transfer inlet 322and a section transfer outlet 324 which form a fluid inlet and fluidoutlet into the modular ring 312. The manifold 320 also generallyinclude a manifold inlet 326 and a manifold outlet 328 into which theflow tube 314 is preferably secured with fluid tight seals.

[0067] Generally, a plurality of modular rings 312 are connected to oneanother. The manifolds 320 of the modular rings 312 generally includebolt holes 330 which extend through the manifold for securing onemanifold to another. When the manifolds are joined together, a seal isgenerally placed between the manifolds to ensure a fluid tight seal.

[0068] FIGS. 12-14 show a preferred spool seal, shown generally asreference numeral 350. The spool seal 350 generally includes a generallycylindrical body 352 having a bore 354 through its center. The spoolseal 350 generally includes an annular central ridge 356 and annularterminal ridges 358 proximate to both ends of the cylindrical body 352.The central ridge 356 and terminal ridges 358 form annular channels 360between them. O-rings 362 are generally placed into the channels 360.

[0069] Other types of seals which are already known and in the relevantprior art may be used to form a fluid tight seal between connectedmanifolds. Some of these may include various gaskets, O-rings, swage,compression fittings, and numerous other types of seals which are wellknown to those practicing the art.

[0070] During use, the spool seal 350 is loaded with O-rings, andinserted into the section transfer inlet 322 of the manifold 320. Thespool seal 350 is inserted such that the bore 354 aligns with thesection transfer inlet 322 to allow fluid flow through the bore 354. Onehalf of the spool seal 350 is generally inserted into the sectiontransfer inlet 322 and one half extends outward for insertion into asection transfer outlet of another manifold 324. The correct positioningof the spool seal 350 is generally governed by stops 323 within themanifold 320 as shown in FIG. 11. Once the manifolds 320 are properlyaligned with spool seal 350 connections, bolts (not shown) are generallyput through the aligned bolt holes 330 which extend through themanifolds 320, and tightened.

[0071] The connection between the modular rings 312 is preferably madewith bolts or other nonpermanent means such that the modular rings 312can later be unconnected without destroying the ring or its componentparts. However, swaging, welding, or other permanent means forconnecting the modular rings 312 may be done if additional strength isdesired.

[0072] Each manifold 320 of the heat exchanger is preferably sized,configured, and attached to the adjacent manifolds such that the joinedmanifolds 320 provide sufficient structural rigidity to transport oroperate the heat exchanger with reduced support for the joined tubularsections. The manifolds 320 may be used to join together modular rings312 of different sizes. For example if the reactor 300 were largerthrough one section, a modular ring 312 having a relatively largerdiameter could be used. Each of the flow tubes 314 has a flow path offrom its inlet to its outlet of a defined flow path length, and twodifferent flow tubes 314, connected by a manifold, may have differingflow path lengths.

[0073] The flow tubes 314 of the heat exchanger 310 are spaced andgenerally provide fluid flow within the various flow tubes 314 alongrespective planes substantially parallel to each other. The manifolds350 provide fluid flow in a direction angular to the planes of flow inthe flow tubes 314. The angular direction of flow through the manifolds350 is approximately ninety degrees with respect to the flow in the flowtubes 314.

[0074] The modular rings 312 of the heat exchanger 310 generally includefins 364. The fins 364 are preferably cast aluminum. More specifically,the fin is preferably cast from a material having a high thermalconductivity such as aluminum Alloy 360. The flow tube 312 generally hasan inner surface 366 and an outer surface 368. The fins 364 aregenerally connected to and extending out of the outer surface 368.

[0075] The heat exchanger 310 preferably includes a plurality ofconnected modular rings 312 and the fins 364 of adjacent modular rings312 are preferable offset such that they create more turbulent flow forany fluid flowing over the heat exchanger. The fins 364 are preferablyaxially misaligned between each modular ring 312. FIG. 15 shows a viewof two stacked modular rings 312. The fins 370 from the top modular ringare visible over the flow tube 372. The fins 374 from the bottom modularring are visible only because they are misaligned with those from thetop modular ring.

[0076] Some of the modular rings 312 of the heat exchanger 310 used inthe reactor 300 are preferably wash coated with a PrOx catalyst 365. ThePrOx catalyst 365 preferably adheres well to the modular rings. Forexample, when the fins 364 are cast aluminum, an aluminum oxide layer onthe fin surface is ideal for adhesion of alumina based catalystwashcoating. The catalyst may be any of the well known PrOx catalystsdiscussed elsewhere in this application, or in the prior art. It can beappreciated that when the heat exchanger is used in other types ofapplications, a catalyst other than a PrOx catalyst may be washcoatedonto the modular rings 312. In certain instances it may be beneficial toinclude a wash coated catalyst on an interior surface of the tubularsection of the modular rings.

[0077] The modular nature of the heat exchanger 310 allows for greatflexibility in maintaining a fluid temperature profile within a fluidflow. Individual modular rings 312 may have different properties formother rings on the same heat exchanger. For example, a heat exchangermay include a first modular ring which is wash coated with a PrOxcatalyst, a second modular ring which is not wash coated, and a thirdmodular ring which is again wash coated with a PrOx catalyst. Numerousvariations of this concept immediately come to mind and are well withinthe skill of one of ordinary skill in the art.

[0078] Other properties also may vary between individual modular ringswithin the same heat exchanger. These may include different number offins, spacing between fins, alignment of fins, material comprising thefins, coating on the fins, heat transfer coefficient, surface area,shape of individual fins, size of the individual fins, orientation withrespect to the flow tubes, and type of attachment to the flow tube.

[0079] The reactor 300 of FIG. 7 generally receives reformate gas atapproximately 300° C. to which air is added at the reformate inlet 302.Liquid water generally enters the heat exchanger 310 at the oppositeend, and flows in a countercurrent direction to the reformate. The watergenerally turns to a two-phase water steam mixture with in the heatexchanger 310. The heat exchanger preferably maintains a desirablethermal profile within the reactor 300. Reaction of the reformate ispreferably catalyzed by the PrOx catalyst 365. The now reacted reformateleaves the reactor 300 through reformate outlet 304. One advantage ofthis reactor is it does not generally require additional air inlets,although, the use of them is contemplated as needed.

[0080] The heat exchanger 310 used in conjunction with reactor 300provides a benefit in that it is easily manufactured. First, a tubularconduit of a first metal is formed into a tubular section of the desiredshape and size. The first metal is preferably stainless steel. Thetubular section is shown in FIGS. 16 and 17 with an attached manifold320. The tubular section is placed in a die, and a second metal is castonto an outer surface of the tubular section in the form of fins.Generally, the manifold 320 is not connected to the tubular sectionduring die casting. The second metal is preferably aluminum. The finsare then optionally wash coated with a catalyst for promoting a desiredreaction in a heat transfer fluid intended to contact the fins duringheat transfer operations. The final step in assembling the heatexchanger 310 is connecting the tubular sections to a connector andconnecting at least two of the tubular sections together with theconnector. The number of tubular sections connected together will varydepending on system requirements.

[0081] Another embodiment of a PrOx reactor according to the presentinvention is shown in FIG. 18 as reference numeral 400. The reactor 400generally includes a plurality of plates 402 which are connected suchthat heat transfer may be performed between two fluids traveling throughchannels 404 formed between adjacent plates 402. In the PrOx reactor 400the two fluids are generally reformate, water, or a water/steam mixture.An interior surface 406 of the plates 402 through which the reformate isrouted is preferably wash coated with a PrOx catalyst 408.Alternatively, a portion of the channel may be packed with a PrOxcatalyst in any of the well know catalyst forms discussed elsewhere inthis application. The reactor 400 is generally understood as a plate andframe type heat exchanger with a reforming capacity provided by theinclusion of a catalyst.

[0082] Flow through the reactor 400 is generally countercurrent as shownin FIG. 19. Reformate generally enters the reactor 400 through areformate inlet 410. Liquid water generally enters the reactor 400through a water inlet 412. The reformate and water/steam then generallyproceed through the reactor exchanging heat through the plates 402 whichseparate the channels 404 through which they flow. The flow through thechannels is preferably directed and made turbulent by the presence ofraised protuberances 414. The pattern of the protuberances 414 may beselected based on the degree to which it is desirable to make the fluidpath tortuous. One system consideration is that additional pressure isrequired to move a fluid through a tortuous fluid path. It is preferableto make the fluid path within a channel 404 travel diagonally across aplate 402. The flow of fluids between channels is done through openings403 in the plates 402.

[0083] The reformate generally exits the reactor through a reformateoutlet 416. The water/steam generally exits the reactor through awater/steam outlet 418. While the two fluids are shown here entering andexiting the reactor 400 through different end plates 420, 422, in otherembodiments, both fluids enter and exit the system through the same endplate 420, and the plates 402 and channels 404 are arranged accordinglyas is well understood by one of ordinary skill in the art.

[0084] While the specific embodiments have been illustrated anddescribed, numerous modifications come to mind without significantlydeparting from the spirit of the invention, and the scope of protectionis only limited by the scope of the accompanying claims.

We claim:
 1. A method of controlling a temperature profile within apreferential oxidation reactor to provide a temperature range within thereactor which favors the selective oxidation of CO in a hydrogen richreformate stream by a preferential oxidation catalyst comprising thesteps of: flowing a stream of a mixture of a hydrogen rich reformate andoxygen over the preferential oxidation catalyst; flowing a stream ofwater proximate to the preferential oxidation catalyst so as the streamof water and the reformate stream passing over the catalyst are in aheat transfer arrangement; and maintaining the stream of water as a twophase stream from a point at which the water reaches its boilingtemperature to a point proximate an outlet from which the stream ofwater exits the reactor.
 2. The method of claim 1, wherein the step ofmaintaining the stream of water as a two phase stream comprises the stepof controlling the flow rate of the water stream.
 3. The method of claim1, further comprising the step of controlling the pressure of the streamof water.
 4. The method of claim 3, wherein the step of controlling thepressure comprises the step of creating pressures in the range of fromabout 1 atmosphere to about 10 atmospheres.
 5. The method of claim 1,wherein the preferential oxidation catalyst is in a form selected fromthe group consisting of: a monolith, a foam, pellets, powder and a washcoat.
 6. The method of claim 5, wherein the step of flowing a stream ofwater further comprises the step of flowing the stream through a heatexchanger wash coated in catalyst.
 7. The method of claim 6, wherein theheat exchanger is a helical tube having contiguous fins or a plate andframe type heat exchanger.
 8. The method of claim 1, wherein thetemperature profile is in the range of from about 75° C. to about 300°C.
 9. The method of claim 1, wherein the temperature profile is in therange of from about 100° C. to about 250° C.
 10. A reactor for theselective oxidation of carbon monoxide in a hydrogen rich reformatestream comprising: a reactor body; an inlet for the addition of areformate stream to the reactor body; at least one oxygen inlet for theaddition of oxygen to the reformate stream; a catalyst suitable forselective oxidation of carbon monoxide, located within the reactor body;a heat exchanger, having an inlet and an outlet, for removing heat fromat least one of the catalyst and the reformate; a stream of waterflowing through said heat exchanger; wherein said stream of water entersthe heat exchanger at least partially as liquid water; and wherein saidstream of water is a two phase mixture of water and steam throughout atleast a portion of the reformate flow path.
 11. The reactor of claim 10,wherein the catalyst is in a form selected from the group consisting ofpellets, foam, a monolith, a powder, and a layer wash-coated onto acomponent of the heat exchanger.
 12. The reactor of claim 10, whereinthe heat exchanger comprises a cooling tube contiguous with thecatalyst.
 13. The reactor of claim 10, wherein the heat exchangercomprises a cooling jacket located proximate to an exterior wall of thereactor.
 14. The reactor of claim 10 wherein the portion of thereformate flow path that is in heat exchange with one of liquid waterand two phase water is substantially equal to the portion of thereformate flow path that contains catalyst.
 15. The reactor of claim 10further comprising: a core in the reactor around which the stream ofreformated is routed; and wherein the catalyst is arranged about thecore.
 16. The reactor of claim 15 wherein the core is hollow.
 17. Thereactor of claim 15, further comprising a unit for processing of ahydrocarbon fuel located within the core.
 18. The reactor of claim 15,wherein the unit comprises a low temperature shift unit.
 19. A reactorfor the selective oxidation of carbon monoxide in a hydrogen richreformate stream, the reactor comprising: a reactor body; an inlet forthe addition of a reformate stream to the reactor body; at least oneinlet for the addition of oxygen to the reformate stream; and asubstrate, wash coated with a catalyst suitable for selective oxidationof carbon monoxide contained within the reactor body wherein thesubstrate is a heat exchanger through which a coolant flows.
 20. Thereactor of claim 19, wherein the cooling medium comprises two phasewater in liquid and gaseous phases.
 21. The reactor of claim 19 whereinthe substrate comprises a cooling tube having fins.
 22. The reactor ofclaim 19, wherein the coolant flows in a generally countercurrentdirection to the direction of flow of the reformate.
 23. The reactor ofclaim 19, wherein the flow of the coolant is in a generally concurrentdirection to the flow of the reformate.
 24. The reactor of claim 19further comprising a core contained within the reactor body around whichthe stream of reformate flows.
 25. The reactor of claim 24 wherein theheat exchanger further comprises a helical tube having fins which isarranged about the core within the reactor body.
 26. The reactor ofclaim 25, further comprising additional inlets through which oxygen isintroduced to the reformate stream.
 27. The reactor of claim 24 whereinthe volume of the core is in the range of from about 10 percent to about95 percent of the volume of the reactor.
 28. A reactor for the selectiveoxidation of carbon monoxide in a hydrogen rich reformate streamcomprising: a reactor body having a reformate stream with a flowdirection therein; a tube carrying the reformate stream having an inletto the reactor body; a tube carrying an oxygen stream having an inlet tothe tube carrying the reformate stream; a first helical tube carrying atwo phase system of water and steam in a direction countercurrent to theflow direction of the reformate stream; a bed of steel shot throughwhich the first helical tube travels and over which the reformate streamflows; a first bed of a selective oxidation catalyst located downstreamof the bed of steel shot; a manifold into which the reformate streamflows; a oxygen inlet into the manifold; a second bed of a selectiveoxidation catalyst into which the reformate stream is flowed from themanifold; a second helical tube carrying water in a directioncountercurrent to the direction of flow of the reformate upon exitingthe manifold; a riser extending from the helical tube through the secondbed of catalyst; a second bed of steel shot through which the secondhelical tube travels and over which the reformate stream flows; anoutlet for the reformate stream; and wherein the riser is in fluidcommunication with the first helical tube outside of the reactor body.29. A heat exchanger comprising: two or more tubular sections each withan inlet and an outlet for permitting circulation of a heat exchangefluid through the tubular section; and,a connector between each tubularsection for permitting a flow from the outlet of one tubular section tothe inlet of the next tubular section.
 30. The heat exchanger of claim29 wherein the connectors are adapted and configured to be connected andunconnected nondestructively.
 31. The heat exchanger of claim 30 whereeach connector has a seal to prevent leakage of heat exchange fluid, theseal being adapted to permit disassembly and reassembly of the tubularsections while still providing a seal against leakage.
 32. The heatexchanger of claim 30 wherein the connectors comprise: a manifoldcoupled to each tubular section, each manifold having a manifold inletfor fluid communication with an inlet of the tubular section, and amanifold outlet for fluid communication with the outlet of the sametubular section, each manifold having a section transfer inlet for fluidcommunication from another manifold, and a section transfer outlet forfluid communication to another manifold down stream in the fluid flow.33. The heat exchanger of claim 32 where each manifold has a seal toprevent leakage of heat exchange fluid as it transfers from one manifoldto another adapted to permit disassembly and reassembly of the tubularsections while still providing a seal against leakage.
 34. The heatexchanger of claim 32 wherein the tubular sections are spaced andprovide fluid flow within the tubular section along respective planessubstantially parallel to each other, and the manifolds provide fluidflow in a direction angular to the planes of flow in the tubularsections.
 35. The heat exchanger of claim 34 wherein the angulardirection of flow through the manifolds is approximately 90 degrees withrespect to the flow in the tubular sections.
 36. The heat exchanger ofclaim 32 wherein each manifold is sized, configured, and attached to theadjacent manifolds so that the joined manifolds provide sufficientstructural rigidity to transport or operate the heat exchanger withreduced support for the joined tubular sections.
 37. The heat exchangerof claim 35 wherein each manifold is sized, configured, and attached tothe adjacent manifolds so that the joined manifolds provide sufficientstructural rigidity to transport or operate the heat exchanger withreduced support for the joined tubular sections.
 38. The heat exchangerof claim 29 wherein each of the tubular sections have inner and outersurfaces and at least one of the sections has fins connected to andextending out of its outer surface.
 39. The heat exchanger of claim 30wherein each of the tubular sections have inner and outer surfaces andat least one of the sections has fins connected to and extending out ofits outer surface.
 40. The heat exchanger of claim 31 wherein each ofthe tubular sections have inner and outer surfaces and at least one ofthe sections has fins connected to and extending out of its outersurface.
 41. The heat exchanger of claim 33 wherein each of the tubularsections have inner and outer surfaces and at least one of the sectionshas fins connected to and extending out of its outer surface.
 42. Theheat exchanger of claim 35 wherein each of the tubular sections haveinner and outer surfaces and at least one of the sections has finsconnected to and extending out of its outer surface.
 43. The heatexchanger of claim 36 wherein each of the tubular sections have innerand outer surfaces and at least one of the sections has fins connectedto and extending out of its outer surface.
 44. The heat exchanger ofclaim 37 wherein each of the tubular sections have inner and outersurfaces and at least one of the sections has fins connected to andextending out of its outer surface.
 45. The heat exchanger of claim 38having fins on more than one tubular section and the fins on eachtubular section having parameters including number of fins, spacingbetween fins, alignment of fins, material comprising the fins, coatingon the fins, heat transfer coefficient, surface area, shape ofindividual fins, size of the individual fins, orientation with respectto the tubular section, and type of attachment to the tubular sectionand at least one of the tubular sections have fins which differ from thefins of at least one other tubular section by one or more of theparameters.
 46. The heat exchanger of claim 39 having fins on more thanone tubular section and the fins on each tubular section havingparameters including number of fins, spacing between fins, alignment offins, material comprising the fins, coating on the fins, heat transfercoefficient, surface area, shape of individual fins, size of theindividual fins, orientation with respect to the tubular section, andtype of attachment to the tubular section and at least one of thetubular sections have fins which differ from the fins of at least oneother tubular section by one or more of the parameters.
 47. The heatexchanger of claim 41 having fins on more than one tubular section andthe fins on each tubular section having parameters including number offins, spacing between fins, alignment of fins, material comprising thefins, coating on the fins, heat transfer coefficient, surface area,shape of individual fins, size of the individual fins, orientation withrespect to the tubular section, and type of attachment to the tubularsection and at least one of the tubular sections have fins which differfrom the fins of at least one other tubular section by one or more ofthe parameters.
 48. The heat exchanger of claim 33 having fins on morethan one tubular section and the fins on each tubular section havingparameters including number of fins, spacing between fins, alignment offins, material comprising the fins, coating on the fins, heat transfercoefficient, surface area, shape of individual fins, size of theindividual fins, orientation with respect to the tubular section, andtype of attachment to the tubular section and at least one of thetubular sections have fins which differ from the fins of at least oneother tubular section by one or more of the parameters.
 49. The heatexchanger of claim 29 wherein at least one of the tubular sections haveinner and outer surfaces and at least one of the inner or outer surfacesis coated with a catalyst for promoting a reaction within the heattransfer fluid.
 50. The heat exchanger of claim 46 wherein the fins aredie cast onto the outer surface of the tubular section.
 51. The heatexchanger of claim 38 wherein the fins are die cast onto the outersurface of the tubular section.
 52. The heat exchanger of claim 41wherein the fins are die cast onto the outer surface of the tubularsection.
 53. The heat exchanger of claim 41 wherein the tubular sectionis stainless steel and the fins are aluminum.
 54. The heat exchanger ofclaim 50 wherein the fins on one of the tubular sections is misalignedwith respect to the fins on another tubular section in a mannersufficient to increase turbulence in the flow of a fluid passing overthe fins of both tubular sections.
 55. The heat exchanger of claim 29wherein each tubular section has a flow path of from its inlet to itsoutlet of a defined flow path length, and at least two of the tubularsections have differing flow path lengths.
 56. The heat exchanger ofclaim 30 wherein each tubular section has a flow path of from its inletto its outlet of a defined flow path length, and at least two of thetubular sections have differing flow path lengths.
 57. The heatexchanger of claim 40 wherein each tubular section has a flow path offrom its inlet to its outlet of a defined flow path length, and at leasttwo of the tubular sections have differing flow path lengths.
 58. Theheat exchanger of claim 41 wherein each tubular section has a flow pathof from its inlet to its outlet of a defined flow path length, and atleast two of the tubular sections have differing flow path lengths. 59.The heat exchanger of claim 38 including a catalyst optionally on thefins, or on the inner surface of the tubular section, or both, forpromoting a desired reaction in a heat exchange fluid intended to flowover the fins or through the tubular section.
 60. The heat exchanger ofclaim 39 including a catalyst optionally on the fins, or on the innersurface of the tubular section, or both, for promoting a desiredreaction in a heat exchange fluid intended to flow over the fins orthrough the tubular section.
 61. The heat exchanger of claim 40including a catalyst optionally on the fins, or on the inner surface ofthe tubular section, or both, for promoting a desired reaction in a heatexchange fluid intended to flow over the fins or through the tubularsection.
 62. The heat exchanger of claim 41 including a catalystoptionally on the fins, or on the inner surface of the tubular section,or both, for promoting a desired reaction in a heat exchange fluidintended to flow over the fins or through the tubular section.
 63. Theheat exchanger of claim 42 including a catalyst optionally on the fins,or on the inner surface of the tubular section, or both, for promoting adesired reaction in a heat exchange fluid intended to flow over the finsor through the tubular section.
 64. The heat exchanger of claim 43including a catalyst optionally on the fins, or on the inner surface ofthe tubular section, or both, for promoting a desired reaction in a heatexchange fluid intended to flow over the fins or through the tubularsection.
 65. The heat exchanger of claim 38 including that the fins aremade at least in part of a catalyst which will promote a desiredreaction in a heat exchange fluid intended to flow over the fins.
 66. Amethod of making a heat exchanger comprising the steps of: a. forming atubular conduit of a first metal into a tubular section; b. placing thetubular section in a die; and, c. casting a second metal onto an outersurface of the tubular section in the form of fins (fins can be anyextending protrusion of any size, shape, orientation with respect toeach other or the tubular section).
 67. The method of claim 66 includingthe step of coating the fins with a catalyst for promoting a desiredreaction in a heat transfer fluid intended to contact the fins duringheat transfer operations.
 68. The method of claim 66 including the stepsof connecting the tubular section to a connector and connecting at leasttwo tubular sections together with the connector.
 69. The method ofclaim 68 including the steps of optionally coating the fins or an innersurface of the tubular section or both with a catalyst for promoting adesired reaction in a heat transfer fluid intended to contact the finsduring heat transfer operations.
 70. The method of claim 66 wherein thefirst metal is different than the second metal.
 71. The method of claim70 wherein the first metal is stainless steel and the second metal is analuminum-based metal.